Bichargeable electrophotograhic light-sensitive materials

ABSTRACT

An electrophotographic light-sensitive material which comprises a support having thereon a light-sensitive layer comprising an insulating resin containing a photoconductive powder dispersed therein, the support being a base paper having a solvent permeation-preventing ability (B) of 0 to 0.5 and having a surface resistance of not more than 1010 ohm/cm2 at 20*C and 40% RH,   in which D1 is the optical density of the dry untreated base paper; D2 is the optical density of the untreated base paper after solvent application; D3 is the optical density of the base paper subjected to conductivity imparting processing; and D4 is the optical density of the base paper subjected to conductivity imparting processing after solvent application.

United States Patent [1 1 Takimoto et al.

[ 51 Aug. 26, 197s.v

[75] Inventors: Masaaki Takimoto; Takashi Saida;

Satoru Honjo, all of Saitama, Japan [73] Assignee: Fuji Photo Film C0., Ltd., Minami Ashigara, Japan [22] Filed: Dec. 3, 1973 [21] Appl. No.: 421,182

[30] Foreign Application Priority Data Doc. 1, 1972 Japan 47-l20459 Dec. 1, 1972 Japan 47420461 [52] US. Cl 96/L7; 96/1 R; 96/1 C; 96/l.5; 96/1.6; 96/1.8 [51] Int. Cl. G03G 5/08 [58] Field of Search 96/1.5, 1.7, 1.8, 1.6

[56] References Cited UNITED STATES PATENTS 3,591,374 7/1971 Sens 96/l.6 3,684,548 8/1972 Coutois 96/l.6

FOREIGN PATENTS OR APPLICATIONS 4,326,710 11/1968 Japan ..96/l.6

1,814,644 7/1969 Germany 96/1 .5

Primary ExaminerRoland E. Martin, Jr. Attorney, Agent, or FirmSughrue, Rothwell, Mion, Zinn and Macpeak 5 7 ABSTRACT An electrophotographic light-sensitive material which comprises a support having thereon a light-sensitive layer comprising an insulating resin containing a pho-'- toconductive powder dispersed therein, the support being a base paper having a solvent perrneation'-; -j

preventing ability (B) of O to 0.5 and having a surface resistance of not more than 10 ohm/cm at 20C and wherein B (D, D 3 4)/ 1 2 in which D is the optical density of the dry untreated base 11' Claims, 1 Drawing Figure BICHARGEABLE ELECTROPHOTOGRAHIC LIGHT-SENSITIVE MATERIALS BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotograhpic light-sensitive material, which comprises a support having provided thereon a light-sensitive layer capable of being charged positively or negatively comprising an insulating resin such as a vinyl chloride-vinyl acetate copolymer containing a photoconductive powder such as zinc oxide dispersed therein, with the support being a base paper having a low ability to prevent solvent permeation and having been subjected to a processing to impart conductivity.

2. Description of the Prior Art In general, an electrophotographic light-sensitive layer comprising an insulating resin containing a photoconductive power dispersed therein is provided on a base paper having been subjected to processing which imparts conductivity. It is well known to use as such a base paper, an ordinary paper such as a bond paper, a printing paper, etc., a vellum paper, an art paper, a baryta paper, a tracing paper, etc., after subjecting them to processing which imparts conductivity. At the same time, these base papers are subjected to processing to impart the ability to prevent solvent permeation in order to make the light-sensitive layer uniform and to improve the image quality. Many developmentprocessing machines are designed for light-sensitive papers manufactured by using the above-described base papers. In the case of employing a liquid development system, it has been necessary to prevent the surface of the light-sensitive papers from coming into contact, in a non-dried state after development, with driving devices such as rollers as much as possible. Also, as to the squeezing rollers for removing the excess amount of developer after development processing, many restraints have been imposed on the materials, pressures to be applied, and the like.

That is, development-processing machines must be designed so as to remove, as much as possible, defects in which toner particles after adhering to the surface of a light-sensitive layer in the development processing from being transferred to the rollers or a like device due to the uniformity of the surface of the lightsensitive layer and then re-transferred to a different area of the surface of the light-sensitive layer, or in which the developed image is blurred by slippage between the light-sensitive layer and the rollers.

It is needless to say that such defects can be removed to some extent by improving the development processing machine itself. However, the abovedescribed limitations imposed on the developmentprocessing machine can be greatly reduced by modifying the light-sensitive material used.

From this viewpoint, providing, the light-sensitive layer with a coarse surface would appear to be effective for removing the above-described defects.

In general, a zinc oxide-resin dispersion system light sensitive material is used to obtain a light sensitive resin which can be negatively charged. However, a lightsensitive material capable of being charged both positively and negatively would enable both negative work and positive work using a toner having the same polarity by merely changing the charge polarity. In the case of conducting both negative work and positive work using a light-sensitive material capable of being charged only negatively, the developer must be changed, which is therefore very inconvenient. In addition, in a liquid system developing apparatus, it is not desirable for a positive toner and a negative toner to be present together even in a small amount. Such often adversely affects the liquid-supplying apparatus and makes the dispersion of the developer itself unstable in the apparatus.

It is, therefore, a primary object of the present invention to provide an electrophotographic light-sensitive material having a coarse surface or surfaces.

Another object of the present invention is to determine in the production of electrophotographic lightsensitive materials, those conditions under which very favorable electrophotographic properties can be obtained.

Another object of the present invention is to provide a zinc oxide-resin dispersion system light-sensitive material capable of being used in a manner of both negative charge and positive charge.

SUMMARY OF THE INVENTION The above-described objects of the present invention can be attained by using, as a base paper. a paper on which at least one surface has been processed to impart an ability to prevent solvent permeation, whereby the ability to prevent solvent permeation (defined hereinafter) is to O to 0.5, preferably, 0 to 0.3, and which surface has a surface resistance of not more than 10 ohm/cm (20C, 40% RH), and then providing on the above-described processed surface a light-sensitive layer comprising an insulating resin containing a photoconductive powder dispersed therein.

In a preferred embodiment of the invention the lightsensitive layer provided comprises an insulating resin of a vinyl chloride-vinyl acetate copolymer containing 55 to by weight of vinyl chloride component and a photoconductive zinc oxide is dispersed in the vinyl chloride-vinyl acetate copolymer.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING The FIGURE illustrates the method for measuring the ability to prevent solvent permeation employed in the present invention, wherein numeral 1 denotes a sample disk paper piece, 2 a metallic cylinder, 3 a photoelectric cell, 4 a ground glass plate and 5 a tungsten lamp.

DETAILED DESCRIPTION OF THE INVENTION An advantage of the electrophotographic lightsensitive material having a coarse surface or surfaces, is that it reduces the restrictions on designing a development-processing machine, as is described before. In addition, the surface of the light-sensitive paper appears and feels more like usual paper. In particular, since a considerable amount of a coating solution of light-sensitive layer permeates into the paper, the electrophotographic light-sensitive material in accordance with the present invention gives the impression that it is far more like a usual paper as compared with the electrophotographic light-sensitive papers commercially available at present.

The present invention will be now described in greater detail by comparing the electrophotographic light-sensitive paper of the present invention with a 3 presently commercially available electrophotographic light-sensitive paper using zinc oxide.

As was described before, an ordinary paper, an art paper, a baryta paper or a tracing paper can be used as the base paper for an electrophotographic lightsensitive paper. Of these, a tracing paper inherently has such a high ability to prevent solvent permeation that it is difficult to use in the present invention. An art paper and a baryta paper are prepared by coating a clay layer and a baryta layerbresp ectively on a base paper. In this specification, they are considered to be coated papers in the sense that they are papers having a pigment coated thereon. Coated papers are prepared by coating an inorganic white pigment such as clay, bar- .ium sulfate, k aolin, titanium oxide or the like dispersed in water-soluble materials such as casein, starch, gelatin, polyvinyl alcohol, or in a water emulsion of a styrenebutadiene copolymer, vinyl acetate, etc. Of these coated papers, the present invention is applicable to those which have a small ability to prevent solvent permeation. With the so-called paper, i.e.. papers which are capable of being treatedas a paper of fine quality, the characteristic properties including water resistance and the ability to prevent solvent permeation greatly vary depending upon the amount of size, the kind of sizing agent, the method of sizing, etc. With this in mind, the original papers usable in the present invention are specified in terms of the ability to prevent solvent permeation in addition to the other physical properties of paper. which is defined and determined in a special manner in the present invention.

The principle of the method of measuring the solvent permeation-preventing ability, to be described hereinafter, is to utilize the phenomenon that the optical density of a paper to transmitting light, particularly parallel light density, is reduced by the permeation of the solvent into the paper.

Strict conditions are usually required for measuring the parallel light density of paper. However, in this case. since a density analogous to the parallel light density is sufficient for the purposes of this invention, the measurement can be conducted in a comparatively simple manner. To be specific, the parallel light density was measured in a manner described below, and the solvent permeation-preventing ability was defined utilizing this density.

The explanation is given with reference to the FIG- URE.

A sample disk paper piece 1 of 12 cm in diameter was prepared. The sample paper piece 1 was placed on one opening of a metallic cylinder 2 of 7 cm in diameter and cm in length. The inside of this cylinder 2 was black to prevent reflection-Then, a photoelectric cell 3, previously standardized, was placed almost at the center of the other end of the cylinder 2 which was closed to light. The effective light-receiving area of the photoelectric cell 3 was a circular area of about 5 cm in diameter. A tungsten lamp 5, with a ground glass plate 4 interposed in the light path, was used as the light source, and the light source was so disposed that the response of the photoconductive cell was about 2,000 lux without a sample placed on the cylinder and in the light path.

The ability to prevent solvent permeation was defined and determined by treating the results obtained using the above-described measuring system as follows.

4 First, the optical density was'mcasured with respect to a paper which had not been subjected to processing to impart conductivity and to processing to prevent solvent permeation, and the thus measured optical density was represented as D,. Then. 1 ml of xylene was sprayed over one surface of the sample so that it spread as uniform as possible and, after 10 seconds, any excess amount of xylene was blotted with filter paper. Immediately, the optical density of the sample was measured, which was represented as D The greater the value of D D the greater is the degree of solvent permeation. The above-described measurements were conducted with respect to non-processed paper. The results with important original papers are given in Table l. Additionally, xylene was selected as a representative solvent since it is frequently used as a solvent for applying electrophotographic light-sensitive layers and is comparatively low in vaporizing rate.

For the art paper and baryta paper. I ml of xylene was sprayed over the coated surface thereof.

From the results given in Table 1, it can be seen that solvent permeation of tracing paper is the smallest. In order to ensure the significance of this measuring method, an accompanying incidental condition is that D, D be greater than 0.2. That is, papers into which a solvent permeates with difficulty such as tracing paper, are not included in the scope of the present invention.

in preparing electrophotographic light-sensitive materials using these original papers as a base paper, it is well known to make them conductive so that they can be used even under low humidity conditions. The present invention provides a process for producing an electrophotographic material having a coarse surface or surfaces and excellent properties, as a result of examining the method and the conditions for rendering papers conductive. That is, the conditions of the present invention, although defined in terms of the variation in the optical density of papers measured by the abovedescribed method, reflect the degree to which solvent permeation into the papers is prevented.

Next, one surface of each of these original papers was rendered conductive, and the optical density of the thus processed surface was measured according to the method described hereinbefore. The optical densities before and after the xylene-treatment are represented as D, and D respectively. The results obtained with an ordinary paper (64 g/m"), vellum paper and art paper (1 10 g/m'-) are shown in Table 2.

Additionally, polyvinylbenzyltrimethylammonium chloride was used as the agent imparting conductivity, hereinafter conductivity-imparting agent."

Table 2 King of Solvent for Amount D D, B** Original Conductivity- Coated Paper lmparting Agent (g/m") Ordinary Paper Water 0.5 [.54 1.12 0.22 (Felt Side) Water/Methanol 0.7 1.50 1.05 0.16

(l/l) Solution*** Vellum Paper* Water 0.5 L38 0.90 0.095

" Water/Methanol 0.7 1.36 0.90 013 (Ill) Solution Art Paper Water 0.3 [.67 1.24 0.12 (Art Side) Water/Methanol 0.5 L67 1.24 0.12

( /l Solution *No differences were observed between the surface and the opposite surface thereof.

( l 2) fl -l) =l l B The B value given in Table l is defined as the solvent permeation-preventing ability herein in the present invention. For those materials which have absolutely no solvent permeation-preventing ability, B equals zero, while with those materials which have large solvent permeation-preventing ability, B equals about 1.0.

The variations in D and D correspond to the variation in the optical density of paper caused by the processing to impart conductivity. However, when the amount of processing is small, D and D can be considered to be almost the same.

Where D and D can be considered to be almost the same, any increase in the B value depends upon an increase in D,. That is, if the processing to impart conductivity also serves to prevent the permeation ofa solvent, D increases and, therefore, the B value increases. However, if solvent permeates through the film of conductivity-imparting agent into the paper in a pinhole-like condition, areas where optical density is low partly appear. Thus, such areas exist at random in the sample disk paper of 12 cm in diameter. Therefore, when a conductivity-imparting film in which pinholes tend to be formed, i.e., into which a solvent can easily permeate, is formed, the areas where the optical density is low become large and, as a result, the average optical density of sample paper piece or D is reduced.

Commercially available zinc oxide-containing lightsensitive papers are made conductive so that the B value becomes about 1.0, and efforts have been made to prevent as much as possible the permeation of the coating solution of the light-sensitive layer into the base paper. In the present invention, however, it is necessary to use .a base paper whose B value is within the range of from O to 0.5 for the following reasons. That is, if the B value is greater than 0.5. unevenness appears in the almost smooth surface of the light-sensitive layer, and thus it becomes impossible to render the surface of light-sensitive layer coarse, which is an object of the present invention. With a base paper of a B value of about 1, since the light-sensitive layer coating solution is spread or distributed comparatively uniformly on the surface of the base paper, the pattern of cellulose fibers contained in base paper is observed on the surface of the light-sensitive layer. On the other hand, the surface of light-sensitive layer in accordance with the present invention having a B value of 0 to 0.5 advantageously forms coarse surface, since the coating solution permeates into the space between the fibers in the paper and the light-sensitive layer is formed as an aggregation of continuous islands.

The surface condition can of course vary depending upon the viscosity of the light-sensitive layer coating solution. However. a coating solution having a viscosity of not more than 300 C.P. which is usually used can provide sufficiently satisfactory results.

According to the results given in Table 2, art paper, baryta paper, etc. are also included in the scope of the present invention as far as the B value is concerned. However, since a light-sensitive layer is formed on the coated surface after it is rendered conductive, the situation becomes a little different from the case of noncoated papers. In conclusion, since the pigment coated surface is smoother than that of the base paper and has smaller depressions or hollows, the lightsensitive layer coating solution permeates extremely uniformly into the coated surface to form an almost smooth surface.

As an original paper which can be used in the present invention, non-coated papers such as an ordinary paper, a vellum paper, a Japanese paper and the like are preferable. However, those coated papers in which the amount coated is small can also be used.

In the present invention, the selection of the original paper is important. In addition, a conductivityimparting agent and its coating composition is also important.

As the conductivity-imparting agents which can be used in the present invention, polyvinylbenzyltrimethylammonium chloride (e.g., ECR-34 made by the Dow Chemical Co.), conductive polymers (e.g., Conductive Polymer 26], made by the Calgon Corp. and represented by the following structural formula:

wherein n represents a positive integer), colloidal aluminum (c.g., Alumina Sol No. 100, No. 200, No. 300, etc., made by Nissan Chemicals Industries, Ltd.), water-soluble acrylic resins (e.g., 40% aqueous solution of Aron A-22, made by Toa Gosei Chemical Industry Co., Ltd.; viscosity at 25C: 40 50 C.P.; pH: 8.0 9.0), polyvinylbenzenesulfonates, quaternary ammonium salts (e.g., having the following structural formula;

CH n

wherein n represents a positive integer), and the like are suitable. These agents can be used alone or in combination. In addition, they can be used together with substances having good film-forming properties, such as polyvinyl alcohol, casein, starch, vinyl acetatestyrene-butadiene copolymer, etc., in a weight ratio of about /10 to 8/2, preferably 0/10 to 7/3 of the agent to the binder, on condition that the solvent permeationpreventing ability B value of the base paper be controlled within the range of O to 0.5 at least on the one surface of the paper. Furthermore, white pigments such as clay, kaolin, titanium oxide, barium sulfate, etc. can also be added under the same conditions described as above. These white pigments may optionally be added up to times the weight of the conductivity-imparting agent (calculated as solid).

Since the preferred surface resistance of the base paper is not more than 10 ohm/cm original papers must be processed with these conductivity-imparting agents to the extent that the solvent permeationpreventing ability is controlled within the required range.

Also, in using a conductivity-imparting agent having a comparatively good film-forming property, such as Conductive Polymer 261 made by the Calgon Corp. to satisfy the above-described requirements, the following techniques are necessary. That is, it is advantageously to reduce the film forming ability of the polymer, for example, by diluting the aqueous solution of this polymer with water to thereby provide an extremely thin coating, or by diluting the polymer aqueous solution with both water and methanol to help the polymer penetrate into the original paper. In addition, a polymer latex or pigment can be added and kneaded to reduce the film forming ability. From this viewpoint, conductivity-imparting agents having a low film-forming property, such as colloidal alumina, are convenient. In using the above-described conductivity-imparting agents, the necessary conditions in the present invention can be satisfied with ease by controlling the diluting method and coated amount.

As preferred embodiments of the present invention, the conductivity-imparting agent can be introduced into the original paper by a size press, or can be introduced thereinto from the opposite side on which a light-sensitive layer is provided.

Although the surface of the base paper on which surface the electrophotographic light-sensitive layer is provided must have a solvent permeation-preventing ability B-value ofO to 0.5, it is not necessary for the opposite surface to satisfy this requirement. In obtaining images using a liquid development system, the opposite surface is favorably processed so that the 8 value becomes about ].0, and this surface is preferably processed to make it conductive.

The photoconductive powder which can be used for the electrophotographic light-sensitive material of the present invention is an inorganic photoconductive powder such as zinc oxide, zinc sulfide, titanium dioxide, cadmium sulfide, cadmium carbonate, indium (III) oxide (ln O etc. These can be used alone or in combination.

Many film-forming resin binders are known. Specific examples thereof include vinyl chloride-vinyl acetate copolymers, styrene-butadiene copolymers, styrenebutyl methacrylate copolymers, polyalkyl methacrylates, polyalkyl acrylates, polyvinyl acetate, polyvinyl butyral, alkyd resins, silicone resins, epoxy resins epoxy ester resins, and the like. In addition, those prepared by cross-linking binary, ternary or quaternary copolymers with polyisocyanates, with the copolymer being prepared from a vinyl monomer having a hydroxy group or groups capable of reaction with an isocyanate, and styrene, an alkyl methacrylate, an alkyl acrylate or a like monomer, or those prepared by cross-linking an alkyd, an epoxy polyester or the like with a polyisocyanate, are also excellent binders.

In a preferred embodiment of the present invention, a vinyl chloride-vinyl acetate copolymer is used as the insulating resin binder. This copolymer preferably contains 55 to by weight vinyl chloride. This copolymer more preferably contains 55-90% by weight vinyl chloride. If the vinyl chloride content exceeds 95% by weight, the solubility of the copolymer is reduced and a solvent having strong dissolving ability becomes necessary. On the other hand, if the vinyl chloride content is less than 55%, the insulating property is deteriorated. For these reasons, a vinyl chloride content within the above described range is preferable. Also, it is necessary to adjust the viscosity so that the coating solution is easy to handle. Form this viewpoint, the degree of polymerization of the polymer preferably should not be very high. Copolymers having a suitable degree of polymerization and polymerization ratio can be optionally synthesized to some extent. Suitable copolymers are commercially available under the trade name of Vinylite made by Union Carbide Corp. U.S.A. In Japan too, analogous products are produced and are commercially available. For example, *Denkalac" made by Electro Chemical Industry Co., Ltd. is suitable. Of these copolymers, those a degree of polymerization of about 200 to 500 are preferable.

Vinyl chloride-vinyl acetate copolymers have the defect that, when the support of the light-sensitive layer is soft, curling occurs. However, this disadvantage can be overcome to a considerable extent by using a plasticizer in combination, or by reducing the degree of polymerization of the copolymer. Although the combined use of a plasticizer in the binder resin of the lightsensitizer layer is truly effective to prevent curling, the plasticizer should be used in an amount as small as possible since it deteriorates the dark attenuation characteristic and the light sensitivity. With the light-sensitive material of the present invention, it has been found that, since the light-sensitive layer coating solution permeates into the base paper, the amount of plasticizer which is used to prevent curling can be reduced. In addition, the light-sensitive material of the present invention shows higher sensitivity than the conventional light-sensitive material in which the base paper has been subjected to a conductivity-imparting processing which at the same time provides the paper with a solvent permeation-preventing ability. Therefore, reduction in the amount of plasticizer is extremely preferable, because a light-sensitive material having higher light-sensitivity can be provided.

Many plasticizers can be used in the present invention. However, in employing a liquid development system, ethylphthalyl ethyl glycolate, diphenylmonoorthoxenyl phosphate. etc. as described in British Pat. No. 1,207,037 are preferable from the standpoint of deterioration of a liquid developer due to dissolution of the plasticizer into the liquid developer.

The structural formulae of the above-described plasticizers are shown below:

Ethylphthalyl Ethyl Glycolate;

Diphenylmonoorthoxenyl Phosphate;

(CZQHHOAP) CH OH wherein n represents a positive integer. Of these, those which have an epoxy equivalent (grams resin containing I g. eq. of epoxy group) of not more than 300 are liquid at an ordinary temperatures. These epoxy resins have a melting point of not more than 25C, and are comparatively low in molecular weight, having an epoxy equivalent or not more than 300. Suitable polyhydric phenols for the production of the polycondensates are biphenol A, phenol-formaldehyde prepolymers, etc. Examples are Epikote l 12, Epikote 828", Epikote 834" (made by Shell International Chemicals Corp), ERL-2258 (made by Union Carbide Corp.), Der 321 (made by Dow Chemical International Corp), Araldite GY 250", Arldite GY 255, Araldite CY 260 (made by Ciba Geigy A.G.), and the like. The chemical composition of these epoxy resins is shown in the following table.

Commercial Epoxy Viscosity Approximate Name Value Molecular Wt.

Epikote 812 140-165 0.9-1.5 pOlSes 320 Epikote 828 184-194 120-150 poises 380 Epikote 834 230-270 470 ERL-ZZSS -130 100-500 c.p.s. DER 321 182-192 500-700 e.p.s. Araldite 180-190 90-110 poises GY 250 Araldite 180-190 50-64 poises GY 25S Araldite 180-200 -160 poises GY 260 In employing a dry development system, other plasticizers such as chlorinated paraffin, dibutyl phthalate, dioctyl phthalate, tricresyl phosphate, butylphthalyl butyl glycolate, diallyl phthalate, etc. can be used in addition to the above-described plasticizers.

The amount of the above-described plasticizers, ethylphthalyl ethyl glycolate and diphenylmonoorthoxenyl phosphate, which can be added is about 5 to 25% by weight, preferably 10 to 20% by weight, based on the total weight of the binder. The amount of the liquid polycondensate of the polyhydric phenol and the epichlorohydrin which can be used is about 2 to 35% by weight, preferably 15 to 25% by weight, based on the total weight of the binder. The amount of these additional plasticizers such as chlorinated paraffin, dibutyl phthalate, dioctyl phthalate, tricresyl phosphate, butylphthalyl butyl glycolate, diallyl phthalate, etc., which can be added is about 5 to 25% by weight, preferably 10 to 20% by weight, based on the total weight of the binder.

The aforesaid vinyl chloride-vinyl acetate copolymer is generally used in an amount of about 0.5 to 20 parts by weight of the copolymer per 1 part by weight of zinc oxide.

As is well known, a spectrally sensitizing dye or dyes can be incorporated in the light-sensitive layer. As the sensitizing dyes for inorganic photoconductive powders, many dyes are presently known. In the present invention, all of them can be used. Of the dyes, the xanthene dyes, the triphenylmethane dyes, the anthraquinone dyes, the azo dyes, the cyanine dyes, the merocyanine dyes, etc. are particularly useful.

As the xanthene dyes, C.I. Acid Yellow 73 (C.I. No. 45350). C.I. Acid Red 51 (C.I. No. 45430), C.I. Acid Red 52 (C.I. No. 45100), C.I. Acid Red 87 (C.I. No. 45380), C.I. Acid Red 94 (C.I. No. 45440), etc. can be used. As the triphenylmethane dyes, C.I. Acid Blue 9 (C.I. No. 42090), C.I. Acid Blue 15 (C.I. No. 42645), C.l. Acid Blue 22 (C.I. No. 42755), C.I. Acid Blue 90 (C.I. No. 42655), etc. can be used. As the anthraquinone dyes, C.I. Acid Blue 23 (C.I. No. 61125), C.I. Acid Blue 27 (C.I. No. 61530), etc. can be used. As the azo dyes, C.I. Acid Red 26(C.1.No. 16150). C.I. Acid Red 27 (C.I. No. 16185), etc. can be used. As the cyanine dyes and merocyanine dyes. those having a COONa, -COOK, SO Na, $0 K, etc. group as a substituent can used.

These sensitizing dyes can be added to the lightsensitive layer in an amount of 0.0005 to 2.0 parts by weight, preferably 0.001 to 1.0 part by weight, per 100 parts by weight of the photoconductive substance.

One preferably embodiment of the present invention where zinc oxide is used is to incorporate these sensitiz- This fact provides an extremely novel light-sensitive material which exceeds the objects of the present invention. That is, a light-sensitive material showing different spectral sensitivity depending upon the kind of 5 charge can be realized with ease. Application thereof mg dyes for zinc oxide in the base paper, which can be f Conducted y adding sensitizing y to the rocessin to a multi-color copying material 15 extremely ef ective. p g The present invention will now be illustrated in solution used for imparting conductivity to the base pagreater detail by the following non-limiting examples of per. In this embodiment, extremely specific phenomepreferred embodiments of the present invention. In the non has been found, which leads to a new application 10 following Examples 1 5, zmc oxide was used as the indifferent from the above-described ob ect of the presorganic photoconductive powder. However, other inorent invention. gantc photoconductive substances can be easily substi- That is, when charging negatively, the light-sensitive tuted for the zinc oxide. material prepared as described above only shows a sen- Unless otherwise indicated. all parts, percents and sitivity intrinsic to the zinc oxide-resin dispersion sysl5 ratios, etc. are by weight. tem light-sensitive layer provided on the base paper or, EXAMPLE 1 when a sensitizing dye 1S incorporated therein, a sensi- The surface resistance (20C, 50% RH) and the B tivity of the spectrally sensitized region corresponding value of an ordinary paper (64 g/m were measured to the dye used. On the other hand, when charging posafter subjecting the felt side and the wire side thereof itively, a spectral sensitivity based on the sensitizing 20 (hereinafter referred to as F side and W side, redye used in the conductivity-imparting processing of spectively) to various conductivitydmpartmg processthe base paper is observed in addition to the spectral mgs using wire rod coating. The results obtained are sensitivity observed in the negative charging. Thus, it shown in the following Table 3.

TABLE 3 Sample Side Conducti- Diluent Amount Surface B No. vity- Coated Resistance imparting After Agent Drying (g/m (ohm/cm) 1 F Mixture of Water 1.5 3.5 X 10' 0.9

Polyvinyl alcohol and Conductive Polymer (6:4) 2 F Mixture of Water 0.5 1.6 X 10" 0.5

Polyvinyl Alcohol and Conductive Polymer* (6:4) 3 F Polyvinyl Water 0.7 7.2 X 10 0.4

benzyltrimethyl-ammonium Chloride 4 F Methanol 0.9 6.1 X 10 not more than 0.1 5 F Colloidal Water 0.4 1.5 X 10" Alumina 6 W Mixture of Water 2.5 2.0 X 10 0.9

Polyvinyl Alcohol and Conductive Polymer (6:4) 7 w Water 1.0 5.3 x 10' 0.4 8 W Polyvinyl- Water 0.7 8.3 X107 0.3

benzyltrimethylammonium Chloride 9 W Methanol 0.9 6.1 X 10' not more than 0.1 10 W Colloidal Water 0.4 1.4 X 10 not more Alumina than 0.1

Conductive Polymer lol made by the Calgon Corp.

' By weight should be understood that. in negatively charging the material, the spectral sensitivity based on the dye used in the conductivity-imparting processing of the base paper is extremely low.

in Table 3. although the surface resistance was favorable in every case. the solvent permeation-preventing ability (B) was unsuitable with sample Nos. 1 and 6 in which the B value was greater than 0.5v

EXAMPLE 2 100 Parts by weight of zinc oxide and 24 parts by weight of a 50% by weight xylene solution of a styrenemodified alkyd resin (styresol No. 4400, made by Japan Reichhold Co., Ltd.; Gardner Viscosity: R T. acid value: not more than 8) were placed in a porcelain ball mill together with 50 parts by weight of nebutyl acetate and kneaded for 16 hours. Then. 20 parts by weight of a 40% ethyl acetate solution of a polyisocyanate compound (Desmodur L-75. made by Farbenfabriken Bayer A.G.; a polycondensate of 1 mol of trimethylol propane and 3 mols of tolylenediisocyanate) was added to the resulting suspension and stirred well for the purpose of cross-linking and hardening the styrene-modified alkyd resin. The resulting mixture was then applied to each of the base papers Nos. 1 10 shown in Example 1. The oppositesurface of the base papers Nos. 1 10, on which the light-sensitive layer was not to be provided, was, subjected to the same conductivity-imparting processing as described for sample No. 6. The coating condition was set so that the coated amount after drying became about 30 g/m with base papers Nos. 1 and 6 into which the light-sensitive layer coating solution permeated with difficulty. After coating and drying, these light-sensitive papers were stored at 50C. thermostatically controlled. for 16 hours to acceleratethe hardening of the binder resin. Light-sensitive papers corresponding to base papers Nos. 1 10 are designated as sample Nos. 11 20, respectively. The primary potential (V,,). dark attenuation potential residual ratio after 1 minute (VGO/VO) and the relative photo sensitivity of these samples are EXAMPLE 3 The humidity dependence of the surface resistance of base papers Nos. 9 and 10 given in Example 1 was examined. The results obtained are shown in the following Table 5.

Table Sample Base Paper Surface Resistance (ohm/cm") No. 20C. 20C 20C.

50% RH 40% RH 30% RH 21 Sample No. 9 6.l l0 5.3Xl0 4.5Xl0 22 Sample No.10 1.4Xl0" 9.0Xl0" 9.0Xl0

Light-sensitive papers using as the base paper Sample Nos. 9 and (that is, light-sensitive paper Nos. 19 and provided good images after liquid development at 20C and 30% RH.

EXAMPLE 4 To one surface of a vellum paper (45 g/m (hereinafter referred to as f side") was applied an aqueous solution of polyvinylbenzyltrimethylammonium chloride in a dry coated amount of 0.3 g/m To the opposite surface (hereinafter referred to as r side) was applied an aqueous solution of a mixture of polyvinyl ale ohol/polyvinylbenzyltrimethylammonium chloride (6:4 by weight) in a coated amount of 3 g/m The surface resistance and B value of each of these 25 fand r sides were as shown in the following Table 6.

Table 6 Surface Surface Resistance (ohni/cm'-) B (20C. 407: RH)

fside 1.0 X 10" not more than 0.1 r side 1.3 X 10" 0.9

To parts by weight of zinc oxide and 24 parts by weight of a 50% xylene solution of a styrene-modified alkyd resin (Styresol No. 4400, made by Japan Reichold Co., Ltd.) was added 50 parts by weight of toluene as a solvent and. further, the following dye solution was added thereto.

3-Carboxymethyl-2(3.3- 0.00! part by weight dicyanoacrydcne )-benzothia1.oline Eosine (C.l. Acid Red 87. CI. 0.001 No.45380) Brilliant Blue FCF (C.l. Acid Blue 0.001

9. C.l. No. 42090) Methanol l0 Then. the resulting mixture was kneaded in a porcelain ball mill for 16 hours.

To the thus obtained suspension was added 20 parts by weight of a 40% ethyl acetate solution of a polyisocyanate compound (Desmodur L, made by Farbenfabriken Bayer A.G.) followed by stirring well for the purpose of cross-linking and hardening the styrenemodified alkyd resin. The resulting coating solution was then applied to the fside of the above-described base paper in an amount of 33 g/m When the solution was also applied to the r side under the same conditions for the purposes of comparison, the coated amount became 31 g/m.

The light-sensitive layer provided on either side exhibited sensitivity over the entire visible light range and had good properties. However, the light-sensitive layer provided on the f side showed a high sensitivity than that on the r side by 15%. As to the surface condition, the f side showed a continuous island-like coarse surface while the r side showed a lustrous surface bearing cellulose fiber pattern.

EXAMPLE 5 A conductivity-imparting agent was allowed to permeate into an ordinary paper of 64 g/m" from the felt side for 'the purpose of providing a light-sensitive layer on the wire side. That is, a 30% aqueous solution of polyvinylbenzyltrimethylammonium chloride was diluted to 2% with methanol and applied to the felt side. In this case, it was observed that a considerable amount of the solution reached the wire side. The coated amount was 0.55 g/m After this first processing, an aqueous solution of polyvinyl alcohol/Conductive Polymer 26] (made by Calgon Corp.) was applied thereto in an amount of 1.5 g/m (calculated as solids). The solvent permeation-preventing ability of the wire side was as low as a B value of less than 0.1. The surface resistance of the wire side and the felt side were as shown in Table 7.

To 100 parts by weight of zinc oxide and 20 parts by weight of a vinyl chloride-vinyl acetate copolymer (85:15 molar ratio) was added 90 parts by weight of nbutyl acetate as a solvent. Then, the resulting mixture was kneaded for l6 hours in a porcelain ball mill to obtain a white suspension. When this suspension was .applied to the wire side and the felt side of the abovedescribed base paper under the same conditions as described above, the coated amounts became 34 g/m and 30 g/m (calculated as solids), respectively. As to the surface condition of the lightsensitive layer, the wire side showed a favorable, continuous island-like, coarse surface, while the felt side showed a lustrous, smooth surface through which the cellulose fibers could be seen.

As to the electrophotographic properties, the lightsensitive layer on the wire side, which is in accordance with the present invention, showed a light sensitivity double that of a conventional light-sensitive layer on the felt side.

Also, for the purpose of reference, a base paper was prepared whose felt side alone had been processed with an aqueuous solution of polyvinyl alcohol/Conductive Polymer 261 (made by Calgon Cor.) (6:4 by weight). The thus processed felt side showed a surface resistance of 4.0 X 10 ohm/cm under the conditions of a temperature of 20C and a relative humidity of whereas the non-processed wire side showed a surface resistance of 2 X 10" ohm/cm When light-sensitive layers were provided on both sides'of this base paper, the light-sensitive layer on the felt side showed almost the same sensitivity as above, while the light-sensitive layer on the wire side showed a sensitivity only of that of the felt side light-sensitive layer. Thus, the existen'ce of the conductivity-imparting agent at the wire side, i.e., at the surface of the base paper to be in contact with the light-sensitive layer, was confirmed to be important.

EXAMPLE 6 Ordinar papers (64 g/m were subjected to a conductivity-imparting processing, and the surface resistance (20C, 40%, R.H.) and the solvent permeation-preventing ability B as defined hereinbefore of the papers were measured. The results obtained are shown in Table 8. In Table 8, the same designations of the F side and W side for the felt side and the wire side, respectively, were used. On the surface of each base pawas provided the following light-sensitive layer.

parts by weight of zinc oxide, 33 parts by weight ofa 45% by weight toluene solution of a vinyl chloridevinyl acetate copolymer (70:30 molar ratio) (Denkalac No. 6], made by Electro Chemical Industry Co., Ltd.; polymerization degree: 260), 3.0 parts by weight of ethylphthalyl ethyl glycolate (as a plasticizer) and 100 parts by weight of n-butyl acetate (as a diluent) were placed in a porcelain ball mill and kneaded for 10 hours. The resulting white suspension was applied to each of the above-described 7 base papers in such manner that the coating was 30 g/m (on a solids basis) on 23-W which had high solvent permeation-preventing property. After drying, these samples were thermostatically held at 50C for 20 hours to remove the remaining solvent.

The electrophotographic characteristics measured are shown in Table 9.

Table 8 Sample Conductivity- Dilucnt Amount Surface Re- B No. lmparting Agent Coated sistance (glm (ohm/cm") (20C. 407/ R.H.)

23 F" Polyvinyl Alcohol! Water 2 5 3.5 X l0 more Conductive Polymer than 0.9 26W (6/4) W 2.5 4.0 X H) 0.9 24 F 2.5 3.5 X l0 more than 0.9 F L5 6.3 X l0 0.5 25 F 1.5 5.8 X10" 0.9 w EcR-3'4 Water/ 0.5 6.1 x H) 0.2

Methanol l )ilil 26 F 0.6 3.2 X H)" 0.3 W Polyvinyl Alcoltol/ Water 2. 6.4 X 10" 0.9

ECR-34 (6/4) 27 F 1.5 8 (l X H)" 0.9

W ECR-34 Methanol 0.3 l 5 X it) less than 0.]

Table 8 -Continued Sample Conductivity- Diluent Amount Surface Re- B No. lmparting Agent Coated sistance (g/m'-) (ohm/cm (20C. 407! RH.)

28 F Polyvinyl Alcohol/ Water 1.5 5.8 X 10 0.9

Conductive Polymer 261 (6/4) W Alumi Sol 100 0.4 2.0 X less than 0.1 29 F Polyvinyl Alcohol/ 1.5 5.8 X 10" 0.9

Conductive Polymer 261 (6/4) W No Processing 8.0 X l0 less than 0.1

'Felt side of base paper -Wire side of base paper "Polyt N.N-dimethyl-3,S-methylenepiperidium)chloride made by the Calgon Corp.

'Polyvinylbenzyltrimethylzimmonium chloride made by the Dow Chemical Co. Colloidal alumina made by Nissan Chemicals Industries. Ltd. ""By volume Table 9 Sample Amount Initial Potential Residual Relative No. Coated Potential Ratio V /V, (7:) Sensitivity (glm (V after 1 Minute Negative Positive Dark Decay Charge Charge From Tables 8 and 9, base pape 23 W and 29 W, which had defects in the electrophotographic characteristics of sensitivity or dark decay property, showed too high a solvent permeation-preventing ability, too a high surface resistance, etc. With other base papers, satisfactory results were obtained in every case. Thus, the significance of this embodiment of the present invention was confirmed. With 23- W, a light-sensitive layer having a surface on which cellulose fiber pattern was observed was formed, while with the other papers, favorable continuous, island-like coarse-surfaced lightsensitive layer was formed. 24 W was the limit at which the island-like unevenness became substantially unform.

EXAMPLE7 A polyvinyl lacohol/Conductive Polymer 261 (made by the Calgon Corp.) was applied to the felt side of an ordinary paper (64 g/m in an amount of 1.5 g/m to thereby impart conductivity, while polyvinylbenzyltrimethylammonium chloride wasapplied to the wire side thereof in an amount of 0.2 g/m to impart conductivity. In thee processing of the wire side, Brilliant Blue FCF was dissolved in the conductivity-imparting agent in sufficient concentration that it was applied to the wire side in an amount of 14 mg/m After the process ing. the wire side had a solvent permeation-preventing ability B value of not more than 0.1 and a surface resistance of 1.5 X 10* ohm/cm (20C. RH).

To the white suspension used in Sample Nos. 23 29 was added a methanol solution of fluorescein and the suspension was stirred well to obtain an orange suspension containing 0.01 part by weight of fluorescein per v 40 trolled, for 10 hours.

When this light-sensitive material was used by negatively charging it, a spectral sensitivity based on the absorption of the fluorescein as well as the sensitivity intrinsic to zinc oxide were observed. On the other hand, when this light-sensitive material was used by positively charging it, a spectral sensitivity based on the absorption of Brilliant Blue as well as the absoprtion intrinsic to zinc oxide was observed. Thus, a light-sensitive material showing different sensitivity using the same material was obtained.

EXAMPLE 8 To one surface of a vellum paper (60 g/m was applied a solution prepared by diluting a 30% by weight aqueous solution of polyvinylbenzyltrimethylammonium chloride to 1% with methanol. This surfaces are designated to as the f side and the opposite side as the r side. After this processing, the physical properties of the f side and the r side were measured. The results obtained are given in Table 10.

Table 10 Surface Resistance 5 Surface of tohm/cm Solvent Pcrmeatiom Base Paper (20C. 407: RH.) preventing Ability: B

f side 15 X l0" less than 0.]

r side 2.0 X l0 less than 0.1

To the white suspension used in Sample Nos. 23 29 was added the following dye solution per 100 parts by weight of zinc oxide and the mixture was stirred well to obtain a colored suspension.

0.01 part by weight When the resulting suspension was applied to the processed fside and r side, a light-sensitive material having continuous island-like, coarse-surfaced was obtained. This light-sensitive material was capable of being charged positively and negatively, and showed a light sensitivity over the entire visible light region.

Also, almost no differences in electrophotographic properties were observed between thefside and the r side.

The present invention has been described in detail by the above example, wherein a primary object of the present invention of making the surface of the lightsensitive layer coarse has been attained by subjecting the surface of base paper to conductivity-imparting processing which provides at the same time only a small solvent permeation-preventing ability. At the same time, as an absolutely unexpectedly novel phenomenon, it has been discovered that the present invention increases the light sensitivity of the light-sensitive layer. As a further secondary effect, the intimate adhesiveness between the light-sensitive layer and the base paper is believed to be greatly improved since the lightsensitive layer coating solution permeates into the base paper.

When a coating solution of a light-sensitive layer is applied to a non-processed original paper, a lightsensitive paper can be obtained which closely approximates the light-sensitive paper of the present invention in surface condition. However, the light sensitivity greatly varies depending upon whether or not the original paper has been subjected to conductivity-imparting processing which provides at the same time only a small solvent permeation-preventing ability. This is one of the greatest advantages of the present invention.

While the invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof.

What is claimed is:

1. An electrophotographic light-sensitive material which can be charged both negatively and positively which comprises a support having thereon a lightsensitive layer comprising a vinyl chloride copolymer containing 55 to 95% by weight of vinyl chloride containing a zinc oxide photoconductive powder dispersed therein, said support being a base paper containing at least one sensitizing dye for said zinc oxide and having a solvent permeation-preventing ability (B) of O to 0.5 and having a surface resistance of not more than 10'" ohm/cm at 20C and 40% RH,

(D1 D2) (D3 D4) wherein B D D2 in which D is the optical density of the dry untreated base paper;

D is the optical density of the untreated base paper after solvent application;

D is the optical density of said base paper subjected to conductivity imparting processing; and

D is the optical density of said base paper subjected to conductivity imparting processing after solvent application, and wherein D D is greater than 0.2.

2. The electrophotographic element of claim 1, wherein said base paper is an ordinary paper, an art paper or a coated paper.

3. The electrophotographic material of claim 1, wherein said base paper has been subjected to conductivity imparting processing.

4. The electrophotographic material of claim 1, wherein said light-sensitive layer contains at least one spectrally sensitizing dye.

5. The electrophotographic material of claim 4, wherein said dye is a xanthene dye, a triphenyl methane dye, an anthraquinone dye, an azo dye, a cyanine dye, or a merocyanine dye.

6. The electrophotographic material of claim 1, wherein said vinyl chloride copolymer is a vinyl chloridevinyl acetate copolymer containing to 90% by weight of vinyl chloride.

7. The electrophotographic material of claim 6, wherein said vinyl chloride-vinyl acetate copolymer resin contains a plasticizer.

8. The electrophotographic material of claim 1, wherein said vinyl chloride-vinyl acetate copolymer is used in an amount of about 0.5 to 20 parts by weight of the copolymer per one part by weight of zinc oxide.

9. The electrophotographic material of claim 1, wherein said sensitizing dye is selected from the group consisting of xanthene, triphenylmethane, anthraquinone, azo, cyanine and merocyanine dyes.

10. The electrophotographic material of claim I,

0 which exhibits a spectral sensitivity due to the sensitizing dye when positively charged.

11. The electrophotographic material of claim 1, wherein said insulating resin is a vinyl chloride-vinyl acetate copolymer. 

1. AN ELECTROPHOTOGRAPHIC LIGHT-SENSITIVE MATERIAL WHICH CAN BE CHARGED BOTH NEGATIVELY AND POSITIVELY WHICH COMPRISES A SUPPORT HAVING THEREON A LIGHT-SENSITIVE LAYER COMPRISING A VINYL CHLORIDE COPOLYMER CONTAINING 55 TO 95% BY WEIGHT OF VINYL CHLORIDE CONTAINING A ZINC OXIDE PHOTOCONDUCTIVE POWDER DISPERSED THEREIN SAID SUPPORT BEING A BASE PAPER CONTAINING AT LEAST ONE SENSITIZING DYE FOR SAID ZINC OXIDE AN HAVING A SOLVENT PERMEATION-PREVENTING ABILITY (B) OF 0 TO 0.5 AND HAVING A SURFACE RESISTANCE OF NOT MORE THAN 1010**10 OHM-CM2 AT 20*C AND 40% RH.
 2. The electrophotographic element of claim 1, wherein said base paper is an ordinary paper, an art paper or a coated paper.
 3. The electrophotographic material of claim 1, wherein said base paper has been subjected to conductivity imparting processing.
 4. The electrophotographic material of claim 1, wherein said light-sensitive layer contains at least one spectrally sensitizing dye.
 5. The electrophotographic material of claim 4, wherein said dye is a xanthene dye, a triphenyl methane dye, an anthraquinone dye, an azo dye, a cyanine dye, or a merocyanine dye.
 6. The electrophotographic material of claim 1, wherein said vinyl chloride copolymer is a vinyl chloridevinyl acetate copolymer containing 55 to 90% by weight of vinyl chloride.
 7. The electrophotographic material of claim 6, wherein said vinyl chloride-vinyl acetate copolymer resin contains a plasticizer.
 8. The electrophotographic material of claim 1, wherein said vinyl chloride-vinyl acetate copolymer is used in an amount of about 0.5 to 20 parts by weight of the copolymer per one part by weight of zinc oxide.
 9. The electrophotographic material of claim 1, wherein said sensitizing dye is selected from the group consisting of xanthene, triphenylmethane, anthraquinone, azo, cyanine and merocyanine dyes.
 10. The electrophotographic material of claim 1, which exhibits a spectral sensitivity due to the sensitizing dye when positively charged.
 11. The electrophotographic material of claim 1, wherein said insulating resin is a vinyl chloride-vinyl acetate copolymer. 